Identification of molecular sequence signatures and methods involving the same

ABSTRACT

Novel means and methods for analyzing hybridization data derived from hybridization assays between a target nucleic acid and differently sequenced polynucleotide probes involve selecting probe sets that define reference sequences for sequence signatures and deriving useful data about the nature of the target nucleic acid molecule based on its hybridization to the probes. The methods are useful for determining whether the target contains a nucleic acid or polypeptide sequence signature, whether the target encodes a member of a gene family, or whether the target is derived from one of any number of genes.

This application is a continuation-in-part of and claims the benefit ofthe filing date of U.S. patent application Ser. No. 08/933,219, filedSep. 18, 1997 which claims the benefit of the filing date of U.S.provisional patent application 60/025,740, filed Sep. 19, 1996, which isincorporated herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to methods and means for rapid screening oftarget nucleic acid molecules for the presence of sequence signatures.In preferred embodiments, hybridization data is processed by aprogrammable digital computer.

Polynucleotide arrays, such as the GeneChip® array (Affymetrix, Inc.,Santa Clara, Calif., USA, can contain many thousands of differentlysequenced polynucleotide probes at feature densities greater than fivehundred thousand per 1 cm². Such arrays enable one to obtain nucleotidesequence information from target nucleic acid molecules. The informationis obtained by performing a hybridization reaction between the targetnucleic acid molecule and the polynucleotide probes on thepolynucleotide array. The location and identity of the probes to whichthe target has hybridized, and the extent of hybridization, isdetermined.

Because hybridization between nucleic acids is a function of theirsequences, analysis of the sequence of the probes to which the targethas hybridized, as well as the extent of hybridization, providesinformation about the sequence of the target molecule.

Because polynucleotide arrays can have many thousands of probes,hybridization reactions create large amounts of raw data for analysis.Already, several ways of processing such data have been developed. Inone application, one examines hybridization between a target moleculeand a set of probes that are based upon a reference nucleotide sequence.Probes in the set to which the target does not hybridize or hybridizesweakly indicate sequences in which the target differs from the referencesequence. Nucleic acid arrays have been used to interrogate singlenucleotide differences between reference and target nucleic acidsequences. Examples include the identification of genetic variants ofinfectious agents, such as HIV, or genes associated with human geneticdiseases, such as cystic fibrosis.

Other ways of obtaining useful information from hybridization data wouldbe of benefit to the scientific and medical communities.

SUMMARY OF THE INVENTION

The present invention involves a hierarchical method of array-basedanalysis in which single nucleotide base determination may or may not beone step. The present invention has several embodiments, many of whichinvolve the determination of a sequence signature. Useful sequencesignatures include polynucleotide or polypeptide sequence signatures,such as those defining protein domains, gene families, different genesin a genome, repeat sequences, or polymorphic forms of a gene. Themethods involve performing hybridization assays between the targetnucleic acid molecules to be screened and polynucleotide arrays designedto identify targets that contain the sequence signatures. The arrayscontain probe sets. The probes in a set, taken together, represent thesequence of the sequence signature, or variations upon that sequence.Thereby, the probes define the reference sequence signature andsequences related to the sequence signature. A hybridization assaybetween the target molecule and the probes in the array generates dataabout which probes the target has hybridized to. The extent ofhybridization may likewise be determined. Computer programs are thenused to process the data. By determining whether the target hashybridized to probes defining one or more reference sequences, or toprobes defining sequences that deviate from the reference sequences, onecan determine whether the target has the same sequence or a sequencesimilar to one or more of the reference sequences. By selectingappropriate reference sequences to put on the array as probes, one candetermine whether a target encodes a particular closely relatedpolypeptide sequence signature, is a member of a gene family, or has thesequence of a particular or closely related gene in the genome. One canalso look at patterns of differences between target and referencesequences to identify novel gene families, new members of gene families,and the like. By identifying the similarities and/or differences betweenthe reference and target sequences, one can also determine the positionon the chromosome of a target nucleic acid molecule.

To determine whether a target nucleic acid molecule contains a sequencesignature, the following steps can be employed: providing apolynucleotide array comprising a set of polynucleotide probes thatdefine the sequence signature; generating hybridization data byperforming a hybridization reaction between the target nucleic acidmolecule and the probes in the set and detecting hybridization betweenthe target nucleic acid molecule and each of the probes in the set; andprocessing the hybridization data to determine whether the targetnucleic acid molecule has the sequence signature. In certainembodiments, the sequence signature is a polypeptide sequence signature;the sequence signature contains variable positions; and the step ofprocessing is performed by a programmable digital computer. In anotherembodiment, if the sequence signature is an amino acid sequencesignature, the array comprises sets of probes that define the degenerateset of nucleotide sequence signatures encoding the polypeptide sequencesignature. In addition, or as an alternative to degenerate probe sets,useful probe sets can contain inosine, other generic bases, or mixturesof A, C, T, G at the 3d position of a codon site. Probe sets can alsocontain sequences that query the presence of polymorphic variants of asequence signature.

One aspect of the invention provides a method of analyzing a nucleicacid sample, comprising selecting a hierarchy of assay techniquescomprising at least a first and second assay. The first assay isselected to provide a determination of the presence or absence orvariant of a first sequence signature and the second assay is selectedto provide a determination of the presence or absence or variant of asecond sequence signature. At least one of the assays employs ahigh-density nucleic acid array. One analyzes the nucleic acid sampleusing the first assay. One may then opt to analyze the nucleic acidsample in a second assay depending upon the results of the first assay.

In a further embodiment, the first or second sequence signature is aconserved region of a gene family. In certain embodiments, the first orsecond sequence signature is a non-conserved region of a gene family.The method can additionally comprise determining the full lengthsequence of said nucleic acid target.

The present invention also provides a method of selecting clones foranalysis. This aspect of the invention provides a support having avariety of clones associated with it. The support is exposed to one ormore polynucleotides under low, medium, or high stringency conditions topermit at least some hybridization between the clones and thepolynucleotides. One identifies the clones that hybridize with thepolynucleotides. Clones selected for analysis are those not identifiedas hybridizing to the polynucleotides. In one embodiment of this method,the support is a high-density nucleic acid array.

Also provided is a method of screening a nucleic acid sample foranalysis. The steps are: providing a sample containing nucleic acids;analyzing whether the sample contains a sequence signature using ahigh-density nucleic acid array; and further analyzing the nucleic acidsample only if that sequence signature is not present.

This invention also provides a method for determining whether a targetmolecule has a sequence from a gene family member. The method involvesproviding a polynucleotide array comprising, for each of at least twodifferent gene family members, a set of polynucleotide probes thatdefine a reference nucleotide sequence from the region of the genefamily member; generating hybridization data by performing ahybridization reaction between the target nucleic acid molecule and theprobes in the sets and detecting hybridization between the targetnucleic acid molecule and each of the probes in the sets; and processingthe hybridization data to determine whether the target nucleic acid hasthe reference sequence from one of the gene family members.

In one embodiment, the step of selecting the target nucleic acidmolecule is performed by determining whether the target hybridizes to anucleic acid probe that hybridizes to a gene encoding the gene familymembers. In another embodiment, the step of processing is performed by aprogrammable digital computer. In another embodiment, the polynucleotidearray further comprises, for each of the gene family members, a probeset defining a highly conserved region of the gene and a probe setdefining a highly variable region of the gene. In a further embodiment,the polynucleotide array further comprises, for each of the gene familymembers, probe sets defining at least two highly conserved regions ofthe gene and probe sets defining at least two highly variable regions ofthe gene. In another embodiment, the reference nucleotide sequence codesfor an amino acid sequence and the array further comprises probe setscapable of defining the different nucleotide sequences encoding theamino acid sequence. In one embodiment, the method further comprises thestep of determining the nucleotide sequence of the target nucleic acidmolecule if the target does not have the chosen signature sequence ofthe gene family member.

In another aspect, the invention provides a computer program product foranalyzing hybridization data comprising: code that receives as input thesequence of a polynucleotide probe in each feature of a polynucleotidearray; code that receives as input reference nucleotide sequences from aplurality of members of a gene family; code that identifies a set offeatures in the polynucleotide array having probes that define thenucleotide sequences; code that receives as input hybridization datafrom a hybridization reaction between a target nucleic acid molecule andpolynucleotide probes in the polynucleotide array; code that processesthe hybridization data to determine whether the target nucleic acidmolecule has a sequence from any of the reference sequences; and acomputer readable medium that stores the codes.

In another aspect, this invention provides a method that involvesdetermining whether a target nucleic acid molecule comprises a sequencefrom one of a set of genes. The method comprises: providing a targetnucleic acid molecule comprising nucleotide sequences from genomic DNA;providing a polynucleotide array comprising, for each gene in the set,polynucleotide probes that define at least one sequence signature from aunique region of the gene; generating hybridization data by performing ahybridization reaction between the target nucleic acid molecule and theprobes in the sets and detecting hybridization between the targetnucleic acid molecule and each of the probes in the sets; and processingthe hybridization data to determine whether the target nucleic acidcomprises a sequence from the unique region of one of the genes. In oneembodiment, the step of processing is performed by a programmabledigital computer. In another embodiment, the unique region of the genecodes for an amino acid sequence. In a further embodiment, thepolynucleotide array further comprises, for each of the unique regions,a set of polynucleotide probes whose sequences define the degenerate setof nucleotide sequences that encode the amino acid sequence. The probesin such embodiments can in addition or as an alternative comprisesequences that contain generic bases such as inosine particularly at thethird codon position. As an even further additional or alternativeoption, polynucleotide probes can have a mixture of A, C, T, and G inthe third codon position within a single feature of a polynucleotidearray.

In another aspect, this invention provides a computer program productfor analyzing hybridization data comprising: code that receives as inputthe sequence of a polynucleotide probe in each feature of apolynucleotide array; code that receives as input sequence signaturesfrom a unique region of a plurality of genes; code that identifies a setof features in the polynucleotide array having probes that define thesequence; code that receives as input hybridization data from ahybridization reaction between a target nucleic acid molecule andpolynucleotide probes in the polynucleotide array; code that processesthe hybridization data to determine whether the target nucleic acidmolecule comprises a sequence from any of the sequence signatures; and acomputer readable medium that stores the codes.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A illustrates an example of a computer system used to executesoftware that can be used to analyze data generated by the presentinvention. FIG. 1A shows a computer system 1 which includes a monitor 3,screen 5, cabinet 7, keyboard 9, and mouse 11. Mouse 11 may have one ormore buttons such as mouse buttons 13. Cabinet 7 houses a CD-ROM drive15 and a hard drive (not shown) that may be utilized to store andretrieve computer programs including code incorporating the presentinvention. Although a CD-ROM 17 is shown as the computer readablestorage medium, other computer readable storage media including floppydisks, DRAM, hard drives, flash tape memory, tape, and the like may beutilized. Cabinet 7 also houses familiar computer components (not shown)such as a processor, memory, and the like.

FIG. 1B shows a system block diagram of computer system 1 used toexecute software that can be used to analyze data generated by thepresent invention. As in FIG. 1A, computer system 1 includes monitor 3and keyboard 9. Computer system 1 further includes subsystems such as acentral processor 102, system memory 104, I/O controller 106, displayadapter 108, removable disk 112, fixed disk 116, network interface 118,and speaker 120. Removable disk 112 is representative of removablecomputer readable media like floppies, tape, CD-ROM, removable harddrive, flash memory, and the like. Fixed disk 116 is representative ofan internal hard drive, DRAM, or the like. Other computer systemssuitable for use with the present invention may include additional orfewer subsystems. For example, another computer system could includemore than one processor 102 (i.e., a multi-processor system) or memorycache.

FIG. 2 depicts tiling to detect signature sequence. The signaturesequence, Asn-Gly-Lys-Ala-Met (SEQ ID NO:2), encompasses a degenerateset of 64 nucleotide sequences that encode it. One of these isATTGGCAAAG CTATG (SEQ ID NO:1). A probe set of 6-mers based onsingle-increment tiling that defines this reference sequence is the setATTGGC (1-6 of SEQ ID NO:1), TTGGCA (2-7 of SEQ ID NO:1), TGGCAA (3-8 ofSEQ ID NO:1), GGCAAA (4-9 of SEQ ID NO:1), GCAAAG (5-10 of SEQ ID NO:1),CAAAGC (6-11 of SEQ ID NO:1), AAAGCT (7-12 of SEQ ID NO:1), AAGCTA (8-13of SEQ ID NO:1), AGCTAT (9-14 of SEQ ID NO:1) and GCTATG (10-15 of SEQID NO:1). Another reference sequence within the degenerate is AACGGAAAGGCAATG (SEQ ID NO:3). A probe set of 6-mers based on single-incrementtiling that defines this sequence is AACGGA (1-6 of SEQ ID NO:3), ACGGAA(2-7 of SEQ ID NO:3), CGGAAA (3-8 of SEQ ID NO:3), GGAAAG (4-9 of SEQ IDNO:3), GAAAGG (5-10 of SEQ ID NO:3), AAAGGC (6-11 of SEQ ID NO:3),AAGGCA (7-12 of SEQ ID NO:3), AGGCAA (8-13 of SEQ ID NO:3), GGCAAT (9-14of SEQ ID NO:3), and GCAATG (10-15 of SEQ ID NO:3).

FIG. 3 depicts an example of a strategy for detecting members of a genefamily. Four regions of three genes in a family are selected assignature sequences (in brackets). The nucleotide sequence signatures ofeach of genes 1, 2 and 3 are defined by probe sets that include probesA, B, C, D (variable region V₁); E, F, G, H (variable region V₂), I, J,K, L (constant region C₁) and M, N, O, P (constant region C₂)

FIG. 4 depicts an example of a strategy for detecting sequencesignatures from a variety of genes. In this example, a polynucleotidearray having 525×525 features is provided that contains probes with allpossible 9-mer sequences. Two polypeptide signature sequences arechecked, Asn-Gly-Lys-Ala-Met (SEQ ID NO:2) and Arg-Arg-Gly-Ser-Phe (SEQID NO:4) (a site recognized by protein kinase A). Particular nucleotidereference sequences ATTGGCAAAG CTATG (SEQ ID NO:1) and CGCCGCGGAA GTTTT(SEQ ID NO:5) are defined by the probe sets a-g and h-n, respectively.The programmable digital computer contains code that identifies thelocation on the array of the features having the defining probes,indicated as letters on the array. In processing the hybridizationinformation, it uses data from the features for the defining sets.

FIG. 5 depicts the nucleotide sequences of four regions of each ofthirty-two members of the TGF-β family of genes. (SEQ ID NOS: 6-38.) Thefirst region of thirty nucleotides is selected from a variable regionjust 5′ of the mature region of the RXXR cleavage site. The secondregion of twenty-four nucleotides is a variable region selected fromnucleotides encoding the first eight amino acids of the mature TGF-βpolypeptide. The third region of twenty-seven nucleotides is selectedfrom the region encoding the CXGXC sequence signature. The fourth regionof eighteen nucleotides is selected from the region encoding the CXCconserved motif at the end of the mature coding region of TGF-β. The farright column indicates the clone name from which the sequences wereselected.

FIG. 6 shows results of a hybridization assay between DNA from TGF-βclones hBMP-7 and hBMP-5 and an array tiled with the sequences describedin FIG. 5 using single-increment and trellis tiling for all ninety-ninebases in the four sequence regions of each of the thirty-two TGF-βclones.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

As used herein, the following terms have the following meanings.

The term “complementary” refers to the topological compatibility ormatching together of interacting surfaces of a probe molecule and itstarget. Thus, the target and its probe can be described ascomplementary, and furthermore, the contact surface characteristics arecomplementary to each other. Complementary includes base complementarysuch as G is complementary to C and A is the complement of T or U in thegenetic code. Complementary also includes other forms of ligand-receptor(also known as ligand-anti-ligand) interactions, such as between othertypes of receptors and their agonists, antagonists, and other moleculesthat bind thereto or show some affinity therefor.

The term “probe” includes a surface-immobilized polynucleotide or otherpolymer that can be recognized by a particular target. Depending oncontext, the term “probe” refers both to individual polynucleotidemolecules and to the collection of same-sequence polynucleotidemolecules surface-immobilized at a discrete physical location. Probe andtarget are often used interchangeably depending upon the context; aprobe can bind or become associated with a target as part of aligand-anti-ligand pair. The probes and targets of the present inventioncan comprise the nucleic acid bases as found in nature or analogsthereof.

The term “target” refers to a molecule of interest. The probe is usefulin obtaining information about the target: whether the target has anaffinity for a given probe. Targets may be naturally-occurring orman-made nucleic acid molecules. Also, they can be employed in theirunaltered state or as aggregates with other species. Targets may beassociated, covalently or noncovalently, to a binding member, eitherdirectly or via a specific binding substance. Targets are sometimesreferred to in the art as anti-probes. A “Probe-Target Pair” is formedwhen two macromolecules have combined through molecular recognition toform a complex.

A target molecule can hybridize to a probe set derived from a referencesequence which is complementary to that of the target. Therefor, thesequence of the probe (and the reference sequence) will be thecomplement of the sequence of the target molecule. Under certainconditions, a target molecule may also hybridize to a probe set defininga reference sequence which is partially complementary to that of thetarget. However, for ease of comparison, the same sequence will be usedto represent a target and the probe and/or reference sequence to whichit will hybridize.

The term “feature” refers to an area of a substrate having a collectionof substantially same-sequence, surface-immobilized polynucleotideprobes. Generally, one feature is different than another feature if theprobes of the different features have substantially different nucleotidesequences. Certain features, however, can be designed to have mixturesof sequences for example to query the 3 position of a codon sequence. Inthe context of light-directed polynucleotide synthesis, for example, afeature is a spatially-addressable synthesis site. See U.S. Pat. Nos.5,384,261; 5,143,854; 5,510,270; 5,593,139; 5,634,734; and WO/95/11995.

The term “polynucleotide array” refers to a substrate havingpolynucleotide probes with different, known sequences, at discrete,known locations associated with its surface. Polynucleotide arrays haveat least two different features and a density of at least five hundredfeatures per square cm. In certain embodiments the arrays can have adensity of about 625, at least one thousand, at least 10 thousand, atleast 100 thousand, at least one million or at least 10 million featuresper square cm. The substrate can be, merely by way of example, siliconor glass and can have the thickness of a glass microscope slide or aglass cover slip. Substrates that are transparent to light are usefulwhen the method of performing an assay on the chip involves opticaldetection. The term also refers to a probe array and the substrate towhich it is attached that form part of a wafer.

“High-density polynucleotide arrays” contain at least 400 differentpolynucleotide sequences per cm².

To “screen” means to analyze a sample or target for certaincharacteristics. One often screens samples to narrow the pool ofmaterial that is subjected to further analysis. The assay utilized toscreen will be a function of the characteristic that one wants toidentify. For example, one can screen using any of the followingillustrative methods: immunological methods such as antibody assays,functional assays to see if a starting material exhibits a biologicalproperty such as enzyme activity or activity associated with certaincell types, hybridization assays, chemical assays, NMR, massspectroscopy, chromatography, electron spin resonance, isoelectricfocusing, electrophoresis, and the like. Useful screening assays includecombinations of these methods performed sequentially or at the sametime. It will be apparent to those skilled in the arts that Northern,Southern, and Western blotting and various other methods including butnot limited to PCR-based screens, ligation-reaction-based screens,hybridization based screens, size based screens, or affinity-basedscreens can be employed.

The term “pre-screen” means a screening step that takes place beforeanother step. As used herein, the terms screen and pre-screen can attimes be used interchangeably.

The term “sequence” refers, depending on context, to the nucleotide(base) sequence of a nucleic acid or the amino acid sequence of apolypeptide.

The term “nucleic acid sequence signature” refers to a chosen orreference nucleotide sequence. Sequence signatures include nucleotidesequences at most 300, 250, 200, 150, 100, 75, 50, 30, 25 or at most 15nucleotides in length. Sequence signatures include sequences less than10, 15, 25, 30, 35, 45, 50, 60, 70, 80, 90, 100, 120, 135, 150, 175,200, 250 and 300 nucleotides long. Sequence signatures also include anycombination of these parameters. Nonlimiting examples of nucleic acidsequence signatures occurring in nature include, e.g., the Hogness Box,the TATA box, a homeobox, the CAAT box and Alu repeat sequences.

The term “polypeptide sequence signature” refers to an amino acidsequence. Amino acids in the sequence signature are selected from thegroup of twenty common amino acids and also include the less commonamino acids. The collection of all amino acid sequences defined by thesequence signature is referred to as the polypeptide “signature set.”

Polypeptide sequence signatures include amino acid sequences in whichthe identity of all, a majority or at least two of the amino acids(common amino acids, uncommon amino acids, or analogues thereof) isfixed. A sequence signature can be chosen to be fixed or variable.Sequence signatures also include amino acid sequences in which the setof amino acids that can occupy a variable position is selected from atmost 15, at most 10, at most 5 or at most 2 of the twenty common aminoacids. Other amino acids, including those known to those skilled in thebiochemical arts as the less common amino acids, are also included.Polypeptide sequence signatures also include amino acid sequences beingat most 300, 250, 200, 175, 150, 100, at most 50, at most 10 or at most5 amino acids in length. Polypeptide sequence signatures also includesequences less than 275, 225, 180, 140, 120, 100, 90, 800, 70, 50, 40,30, 20, 10, or 5 amino acids in length. Polypeptide sequence signaturesalso include any combination of these parameters. Examples ofpolypeptide sequence signatures include the zinc finger motif and otherstructural motifs including without limitation coils, loops, helices,turns, leucine zippers, symmetric dimer features, and combinationsthereof; the consensus recognition sequence for protein kinase A, forbeta globins, for immunoglobulins, for the TGF beta superfamily, for DNAbinding proteins, steroid-hormone receptor superfamily, to name a few.

The term “gene” refers to a genomic nucleic acid sequence at aparticular genetic locus whose exons encode a polypeptide.

The term “region” when referring to a gene, means a sub-sequence of atleast 9 contiguous nucleotides within the nucleotide sequence of thegene or a sub-sequence of at least 3 amino acids within the amino acidsequence of a polypeptide encoded by a gene.

The term “unique region” refers to a sub-sequence that is notsubstantially shared by two genes.

The term “gene family” refers to a collection of genes encoding at leastone polypeptide domain whose amino acid sequences have at least 25%sequence identity over a comparison window of at least 20 amino acids.Such domains are related through common ancestry as a result of geneduplication or evolution. Many polypeptide domains are known in the artincluding, for example, the EGF domain, the immunoglobulin domain, thefibronectin type III domain, the cadherin-like domain, death effectordomains (DED) to name a few. See, Vaux, D. L., Cell, Vol. 90, pp.389-390 (1997) and in its entirety; Molecular Biology of the Cell, 3rdEd., Alberts et al., (1994). Protein domains are also discussed in moredetail in R. F. Doolittle, Annu. Rev. Biochem., (1995) 64:287-314.

Gene families frequently encode polypeptides sharing at least one highlyconserved region. Two polypeptides share a “highly conserved region” ifthe polypeptides have a sequence identity of at least 60% over acomparison window of five amino acids, or if they share a sequenceidentity of at least 50% over a comparison window of ten amino acids.

Polypeptide members encoded by a gene family, the protein family, canhave highly variable regions. A “highly variable region” of apolypeptide encoded by a gene family member is a region of ten aminoacids that has less than 30% sequence identity with the same region of apolypeptide of another gene family member. Protein families that can beinterrogated using the present invention include the TNF family, theBCL-2 family, actins, the heat shock proteins, keratins, myosin, proteinkinases, transcription factors, tubulins, egg shell proteins, alphaglobin, beta-like globins, immunoglobulins, ovalbumin, transplantationantigens, visual pigment protein, and vitellogenin as non-limitingexamples. See, Vaux, D. L., Cell, Vol. 90, pp. 389-390 (1997) and in itsentirety; Molecular Biology of the Cell, 3rd Ed., Alberts et al.,(1994); Avise, J. C., Molecular Markers, Natural History and Evolution,Chapman and Hall publishers (1994); Stryer, L., Biochemistry, 3rd. Ed.(1988); and Atassi, M. Z., Molecular Immunology, Marcel Dekker, Inc.(1984).

“Pseudogenes” are genomic regions that do not result in protein productsin the organisms that contain them.

Pseudogenes have sequence similarities to their true gene counterparts.Pseudogenes may arise from duplication of ancestral genes except thatmutations contained in or near the pseudogene interfere withtranscription or translation. Lodish et al., Molecular Cell Biology,3rd. Ed, Scientific American, Inc., New York, N.Y. (1995). As usedherein, pseudogenes can be members of gene and protein families thatcontain their functional counterparts.

“Tandem repeat genes” or “tandemly repeated genes” encode identical ornearly identical proteins or functional RNAs. The copies can appear oneafter the other separated by spacer regions that can vary within anindividual. Lodish et al., Molecular Cell Biology, 3rd. Ed, ScientificAmerican, Inc., New York, N.Y. (1995). As used herein the tandem repeatgenes are a subset of members of a gene family.

“Tandem repeats” unlike tandem repeat genes can be simply nucleic acidssegments that are repeated but do not necessarily encode protein orfunctional RNAs. These too are subsets of gene families as that term isused herein.

“Simple-Sequence DNA” is largely composed of 5-10 base pair sequencesrepeated in long tandem repeats. Those skilled in the art willappreciate that simple-sequence DNA is often concentrated at certainregions of a chromosome. For example, a large amount of mouse simplesequence DNA is located near centromers. Accordingly, such sequences canbe used as markers and to localize specific chromosomal sites. Lodish etal., Molecular Cell Biology, 3rd. Ed, Scientific American, Inc., NewYork, N.Y. (1995).

“Intermediate repeat DNA” or moderately repeated DNA is dispersedthroughout various genomes: those of mammals, drosophila, and yeast forexample. Certain intermediate repeat sequences are transposable DNAelements. Lodish et al., Molecular Cell Biology, 3rd. Ed, ScientificAmerican, Inc., New York, N.Y. (1995).

“Spacer DNA” has no currently known function other than to separatefunctional DNA sequences. Lodish et al., Molecular Cell Biology, 3rd.Ed, Scientific American, Inc., New York, N.Y. (1995).

A polynucleotide probe has a sequence “selected from” a referencesequence if the sequence of the polynucleotide probe is a sub-sequenceof the reference sequence. For example, the probe ATTGGC (1-6 of SEQ IDNO:1) has a sequence selected from ATTGGCAAAG CTATG (SEQ ID NO:1).

A set of polynucleotide probes “define” a reference sequence if thesequences of the polynucleotide probes are selected from the referencesequence and if, taken together, the sequences of the polynucleotideprobes include the entire sequence of the reference sequence. A probeset also defines sub-sequences within it. For example, the probes ATTGGCand GGCAAA also define the sub-sequence TTGGCA.

The term “tiling strategy” refers to criteria used to select a probe setthat defines a reference sequence or set of reference sequences.

“Block tiling” generally refers to a tiling strategy including a set ofprobes defining a reference sequence in which none of the probes in theset overlap in sequence. For example, the reference sequence ATTGGCAAAGCTATG (SEQ ID NO:1) can be block tiled by the set, ATTGG (1-5 of SEQ IDNO:1), CAAAG (6-10 of SEQ ID NO:1), and CTATG (11-15 of SEQ ID NO:1).

“Single-increment tiling” refers to a tiling strategy including a set ofprobes that defines a reference sequence in which each probe in the setoverlaps in sequence with another probe in the set except for a terminalnucleotide.

For example, the reference sequence ATTGGCAAAG CTATG (SEQ ID NO:1) canbe single-increment tiled by the set ATTGGC (1-6 of SEQ ID NO:1), TTGGCA(2-7 of SEQ ID NO:1), TGGCAA (3-8 of SEQ ID NO:1), GGCAAA (4-9 of SEQ IDNO:1), GCAAAG (5-10 of SEQ ID NO:1), CAAAGC (6-11 of SEQ ID NO:1),AAAGCT (7-12 of SEQ ID NO:1), AAGCTA (8-13 of SEQ ID NO:1), AGCTAT (9-14of SEQ ID NO:1) and GCTATG (10-15 of SEQ ID NO:1).

“Double-increment tiling” refers to a tiling strategy including a set ofprobes that defines a reference sequence in which each probe in the setoverlaps in sequence with another probe in the set except for two,consecutive terminal nucleotides. For example, the reference sequenceATTGGCAAAG CTATG (SEQ ID NO:1) can be double-increment tiled by the setATTGGC (1-6 of SEQ ID NO:1), TGGCAA (3-8 of SEQ ID NO:1), GCAAAG (5-10of SEQ ID NO:1), AAAGCT (7-12 of SEQ ID NO:1), AGCTAT (9-14 of SEQ IDNO:1) and CTATG (11-15 of SEQ ID NO:1).

“Standard tiling” refers to a tiling strategy for a sub-sequence of areference sequence. Standard tiling includes a set of probes as follows.All nucleotide positions in the sub-sequence are designated fixed,except for one, which is designated variable. One probe in the set has(or complements) the sequence of the reference sub-sequence. The otherprobes in the set have the same nucleotide as the reference sub-sequenceat the fixed position, but have a different nucleotide at the variableposition, and no two probes in the set have the same sequence. Thus, forexample, the reference sequence ATTGGCA (1-7 of SEQ ID NO:1) may bestandard tiled with the set ATTGGCA (1-7 of SEQ ID NO:1), ATTaGCA,ATTtGCA and ATTcGCA.

“Standard, single-increment tiling” refers to a tiling strategy thatcombines in a single-increment tiling strategy with a standard tilingstrategy for each probe in the single-increment set. For example, thereference sequence ATTGGCAAA (1-9 of SEQ ID NO:1) can be tiled with astandard, single-increment strategy with the following probe sets:

Reference: ATTGGCAAA (1-9 of SEQ ID NO: 1) Probes: (1) ATTGGCA,(1-7 of SEQ ID NO: 1) ATTaGCA ATTtGCA ATTcGCA (2) TTGGCAA(2-8 of SEQ ID NO: 1) TTGaCAA TTGtCAA TTGcCAA and (3) TGGCAAA,(3-9 of SEQ ID NO: 1) TGGaAAA TGGtAAA TGGgAAA.

Hybridization data derived from arrays including standard,single-increment tiling for a reference sequence is useful inbase-calling—the determination that a base in a target is different thanthe base in the reference sequence, and the identification of thatdifferent base.

The tiling strategy can be carried out by placing probes in adjacentfeatures on the array. For example, probes defining a sequence insingle-increment tiling can be placed in a horizontal row in adjacentfeatures on the array; and probe sets for standard tiling for each ofthe probes in the single-increment set can be placed in a vertical rowbeneath the reference sequence.

However, the power of a programmable digital computer can reduce oreliminate the need for customized tiling. For example, a probe array cancontain probes defining all possible polynucleotide 9-mers. The computercan carry in its memory the location of the feature containing the probehaving any given 9-mer sequence. Then, relying on the referencesequence, the computer can identify the locations of all the probes thatmake up, for example, the single-increment tiling set for the referencesequence. Similarly, the computer can identify the location of all theprobes making up the standard tiling set for each of the probes definingthe reference sequence. Then, in processing hybridization data, thecomputer can be programmed to examine hybridization between target andprobe at each of the feature locations defining the single-increment,standard tiling set.

The term “degenerate set” refers to the set of all nucleotide sequencesthat encode a particular polypeptide sequence signature.

The term “high discrimination hybridization conditions” refers tohybridization conditions in which a single base mismatch can bedetermined.

Stringency conditions useful in the practice of the present inventionare set forth in Sambrook et al., Molecular Cloning: A LaboratoryManual, 2d Ed. (1989).

“Base calling” refers to a process involving comparing the nucleotidesequence of a target molecule with a reference nucleotide sequence andidentifying positions at which the nucleotide in the target molecule isdifferent than the nucleotide in the reference sequence. “ID basecalling” refers to the process of base calling further involvingdetermining the identity of a nucleotide in the target molecule that isdifferent than a nucleotide in the same position of the referencesequence.

A target nucleic acid sequence is of “unknown genetic origin” if it hasnot been identified to derive from a known genetic locus.

II. Description

Nucleic acid arrays have been used to interrogate single nucleotidedifferences between reference and target nucleic acid sequences. Thepresent invention by contrast involves a hierarchical method ofarray-based analysis in which single nucleotide base determination mayor may not be one step. For example, the present invention provides as afirst step (or series of steps) the determination of whether a targetnucleic acid contains a sequence signature. The sequence signature cancomprise, for example, a set of repeat sequences, a conserved regionamong gene family members, or other multinucleotide groupings that areof interest. The possible outcomes are that a target contains the exactsequence signature in its entirety, lacks the sequence signature in itsentirety, or contains one or more variations of the sequence signature.Those outcomes can be used for a variety of purposes: to set up aclassification system for nucleic acids of interest based upon sequencesignatures, to assign nucleic acids to known groupings of existingclassification systems, to determine what if any further analysis isdesired, to decide whether to retain or discard all or portions of anucleic acid sample, and whether special storage or disposal methods arerequired.

One skilled in the art will appreciate that such outcomes areparticularly relevant to diagnosis of patients and in the identificationof disease. For example, one can first determine whether a sequencesignature present in a possible pathogen or set of pathogens is presentin nucleic acids obtained from a patient's body fluids or tissue as afirst step in narrowing down a diagnosis. For example, one can determinewhether a sequence signature of a mycobacterium is present. See PCTApplication No. PCT/US92/02102 (published Aug. 14, 1997, publication No.WO97/29212). Using the methods taught in PCT/US92/02102, one canidentify, for example, the presence of different mycobacterium speciesbased on sequences signatures. Using the hierarchical methods of thepresent invention, if no mycobacterium is present, the presence ofanother suspected pathogen is explored.

The process can be repeated using different arrays having different setsof sequence signatures until the desired level of detail regarding thesequence of the target nucleic acid is obtained. Alternatively, thismultistep process can be carried out in a single experiment on one arrayhaving probes directed to multiple sequence signatures. The methodsdisclosed herein can also be employed using one or more arrays in serialor parallel fashion.

The present invention relies upon the outcomes of first determinationsto make decisions or further determinations until the desired level ofinformation is determined. The present invention also provides a methodof probing for the presence or absence of sequence signatures and theirvariants in a binary or trinary fashion. Binary analysis asks whether aspecific sequence signature is identified or not; a binary determinationis a yes/no determination. A trinary analysis asks whether a specificsequence signature is present, absent, or whether a variant of thatsequence signature is present; a trinary determination is ayes/no/variant determination. One will appreciate that a quaternaryanalysis can also ask whether a variant is absent, and so on. Thehierarchies contemplated by the present invention include a firstdetermination based upon binding of a target to an array followed by atleast one other array-based determination of interest.

In binary and trinary analyses in which the goal is novel genediscovery, often the most useful information is contained in thosesamples that do not contain a particular sequence (a no in both binaryand trinary analysis) or those samples that contain a variant of aparticular sequence (a variant in trinary analysis). When doing genediscovery, it is of enormous benefit to pre-screen nucleic acids forthose that contain a sequence that has already been identified (a yes inbinary or trinary analysis). One can, for example, discard all of thesamples that contain the known sequence signature to focus further studyon only those nucleic acids that do not contain that sequence signature.When looking for new genes, much time, labor, and money is saved bynarrowing the pool of samples for analysis using this embodiment of thepresent invention.

An example of the practice of the present invention involves determiningwhether a set of samples contains a nucleic acid that is a member of agene family. As a first step or first series of steps, one can determinethe level of hybridization between nucleic acids contained in thosesamples and arrayed probes that interrogate the sequence of eitherstrand of a DNA encoding at least a portion of a conserved regionassociated with a gene family of interest. The samples are then dividedaccording to the results. For purposes of illustration, assume that of aset of three patient samples, the nucleic acids derived from thosesamples showed the presence of the entire portion of the probed-forconserved sequence, the absence of the entire portion of the probed-forconserved sequence, and at least one variant of the portion of theprobed-for conserved sequence. The patient samples and/or nucleic acidsderived therefrom are segregated or classified accordingly into newsets, 1, 2, and 3. If a greater level of detail regarding one or more ofthe segregated sets is desired, further analysis is performed. Thefurther analysis can differ for each of the 3 (in this case) sets.

Further inquiry of set 1 can include looking for any remaining portionsof the conserved sequence that were not interrogated in the firststep(s). Based on the results of such further inquiry, set 1 can befurther divided into three subsets: A, B, and C. Those subsets can beanalyzed to determine the presence of other conserved sequences orvariants thereof. The subsets are further divided into threesub-subsets, for example. The sub-subset can be analyzed for thepresence of another sequence signature and so on.

Such an inquiry is particularly useful for identifying new members ofgene families. For example, any samples or sets that contain nucleicacids containing sequence signatures that together identify thosenucleic acids as member of a gene family can be further screened usingarrays that contain probes that query the non-conserved regions of theknown gene family members. The arrays can be tiled to permitidentification of sequence differences at the single nucleotide level sothat the novel sequence of the new family member is obtained.

It will also be appreciated that this method is also beneficial toindustries involving large scale manufacture of polymers. In thebiotechnical arts, for example, large scale recombinant proteinsynthesis can result in mixtures of recombinantly produced polypeptides.In certain cases, for example, E. coli can insert so called “friendly”codons under certain fermentation conditions into some but not all ofthe polypeptide product. One can test recombinant protein for thepresence of sequence signature variants as the first step or series ofsteps in a decision tree. That decision tree can involve the segregationof lots that contain the variants from those that do not. The variantlots can be discarded or further analyzed to the level of detaildesired.

It will also be appreciated that the present invention involves the useof an array, preferably a high density array, in a least one of thesteps of any method taught herein. The other steps may be performedusing techniques known to those skilled in the arts. In addition, thisapplication discusses the invention often in terms of nucleic acidarrays and nucleic acid analysis. Analysis of other materials and theuse of other polymer arrays, including without limitation polypeptideand polysaccharide arrays is contemplated by the present invention.

The hierarchy of analysis taught herein confers several advantages. Onesuch advantage is conferred by looking, for example, at a small segmentof sequence data—the sequence of the signature or sets of signaturesinstead of the full length sequence—to determine what if any furtheranalysis is desired. By taking this hierarchical approach, the time,labor, cost, and amount of materials involved in handling andmanipulating sample for analysis can be reduced.

The present invention not only provides this novel hierarchy ofanalysis, it further teaches that for discovery of previouslyuncharacterized molecules, the most useful information can be derivedfrom analysis of those samples that have been shown to not contain, orsegregated after a screening step to decrease the likelihood ofcontaining previously characterized sequence signatures or partsthereof. For example, a sample that contains a sequence signature or avariant from a conserved region of a gene family but does not containthe unique sequence signatures that characterize the different membersof that gene family likely contains a novel member of the gene family.In such cases, further analysis of that sample is particularlydesirable. For example, in such cases, and at that stage in thehierarchy of analysis, determination of the full length sequence or atleast of the region that differs from the unique region of other membersof the putative gene family is appropriate. Prior to or simultaneouslywith determination of the full length sequence at the single nucleotidelevel, one can obtain the footprint or bar code hybridization pattern.See WO97/29212 and EP Application No. 95307476.2, filed Oct. 20, 1995,published as EP 0717113A2, Jun. 19, 1996. It will be appreciated that atleast in certain circumstances, single nucleotide determination can beinferred from the footprint or other hybridization pattern.

The hierarchical methods of the present invention are particularlyuseful in the identification of gene family members; the discovery ofnew gene family members or other molecules; the identification ofnucleic acid fragments as being from or containing certain regions of agenome (human or otherwise); the handling or disposal of potentiallyhazardous materials including without limitation those containing prionsor nucleic acid materials such as retroviruses; the segregation ofmaterials into different biohazard groupings; epidemiologicalcharacterization and analyses; analysis of recombinantly orenzymatically manufactured biological materials such as nucleic acids(including without limitation antisense agents, ribozymes, promotersequences, control sequences, restriction site sequences, cappedsequences, tailed sequences, branched sequences, methylated sequences,vector sequences, analogues including peptide nucleic acids, and othersequences or varieties) proteins or peptides (including withoutlimitation insulin, growth factors, antibodies, endorphins, enkephalins,and protein or peptide analogues) carbohydrates of all forms andanalogues thereof, proteoglycans, and filementious materials includingwithout limitation those containing fibrins, actins, myosin,tropomyosin, troponin, and meromyosin; quality control and assurance formanufactured biological materials, natural or synthetic polymers, orother chemical materials; the narrowing of a clone pool; and others.

All of the methods discussed herein can include: correlating RNA levelswith gene sequences of interest; the identification and use ofexpression patterns; the narrowing of expression pattern information ina hierarchical fashion; or the selection, including by experimentaldesign, of subsets of particular expression profiles. For example, onecan look for the absence of sequence signatures of enzymes involved in aparticular metabolic pathway. If one or more of the sequence signaturesare missing, one may conduct a second assay for the sequence signaturesof other enzymes that can or are thought to metabolize the excessaccumulation of bioproducts that results from the enzyme deficiencyscreened for in the first assay.

A. Screening Methods

1. Analyzing for Sequence Signatures

In one aspect, this invention provides methods that involve analyzing anucleic acid molecule for the presence of a sequence signature. Suchanalysis involves starting with a polynucleotide array that contains aset of probes that define the sequence signature; generatinghybridization data by performing a hybridization assay between thetarget and the array and detecting hybridization between the target andthe probes in the array, and processing the hybridization data todetermine whether the target contains the sequence signature.

The probes required on the polynucleotide array depend upon the sequencesignature to be analyzed. The sequence signature can be, for example, anamino acid sequence or a nucleotide sequence. The sequence signaturecould define, for example, a polypeptide domain. The sequence signaturecould be a fixed sequence or a consensus sequence in which certain ofthe positions are not fixed. Consider, for example, the consensusrecognition sequence for protein kinase A: RRX(S/T)Z, wherein X is anyamino acid and Z is a hydrophobic amino acid selected from valine,leucine or isoleucine (SEQ ID NO:3). The signature set for this aminoacid sequence comprises 1×1×20×2×3, or 240 different amino acidsequences. The number of nucleotide sequences that encode this signatureset equals the product of the number of codons that encode the possibleamino acids at each position. In this case, a complete degenerate setfor all the amino acid sequences in the signature set contains6×6×61×(6+4)×(4+6+3)=285,480 different reference nucleotide sequences.In contrast, the degenerate set of all possible nucleotide sequencesencoding the single recognition sequence RRGSV (SEQ ID NO:39), is6×6×4×6×4=3456 sequences. For recognition of certain sequencesignatures, a generic array of all possible 8-mers, for examples, can beparticularly useful. See PCT Application No. 97US/01603, filed Jan. 22,1997, PCT publication No. Wo97/17317.

In one embodiment, a polynucleotide array is selected that containsprobe sets defining the complete degenerate set of nucleotide sequencesencoding all possible amino acids in the amino acid signature sequence.However, alternative approaches are possible, depending upon theparticular sort of analysis one wishes to undertake. For example, onemight wish to analyze only a sub-set of the amino acid sequences in thepolypeptide signature set. In this case, one can select a polynucleotidearray whose probe sets define the degenerate sets encoding only thoseamino acid sequences. Or, one may wish to screen for targets havingselected codons encoding all or some of the amino acids in thepolypeptide signature set. In this case, one can select a polynucleotidearray having probe sets that define less than the degenerate set for anyparticular amino acid sequence, e.g., at least 25%, at least 50%, atleast 75% or at least 95% of the degenerate set of sequences encodingthe polypeptide sequence signature. (See FIG. 2.) Combinations of thetwo approaches are also possible. Useful probe sets can also containgeneric bases such as inosine or mixtures of A, C, T, G, or U at theequivalent of the third codon position in the sequence.

One then carries out a hybridization reaction in which the targetnucleic acid sequence is contacted with the polynucleotide probe underhybridization conditions. If the target nucleic acid molecule is verylong, one can optionally break the target into fragments and contact thearray with the fragments. Usually the target or fragments thereof aredetectably labeled so that the positions at which they have hybridizedcan be determined.

After carrying out the hybridization reaction, hybridization is detectedbetween selected probes and the target to generate hybridization data.This data usually reflects the amount of hybridization, as determined bythe strength of the detectable signal (fluorescence for example),between the target and the probes at a particular feature. One can usehigh, intermediate, or low discrimination hybridization conditions asdesired.

The hybridization data is then processed, preferably by programmabledigital computer, to determine whether the target contains a nucleotidereference sequence defined by any probe set. Processing thehybridization information can comprise determining the degree offidelity of hybridization between the target nucleic acid molecule andeach probe in the set, whereby hybridization with high fidelity to allthe probes in the set indicates that the target nucleic acid moleculecontains the sequence signature, and hybridization with high fidelity toa subset of the probes in the set indicates that the target nucleic acidmolecule has part of the sequence signature.

For example, suppose one desired to determine whether a targetpolynucleotide encoded the amino acid sequence RRGSV (SEQ ID NO:39). Asstated above, 3456 nucleotide sequences encode this amino acid sequence.An array can be selected that includes probe sets using asingle-increment tiling strategy defining the degenerate set ofnucleotide sequences that encodes RRGSV (SEQ ID NO:39). Suppose,further, that the target nucleic acid has the sequence CGACGAGGGTCTGTC(SEQ ID NO:40), which encodes RRGSV (SEQ ID NO:39). Under highdiscrimination hybridization conditions, this target sequence wouldhybridize to the single-increment probe set as depicted by asterisk:

Signature:   R  R  S  V  G (SEQ ID NO: 39) Reference:  CGACGAGGGTCTGTC(SEQ ID NO: 40) Probes: *CGACGA  *GACGAG   *ACGAGG    *CGAGGG    *GAGGGT      *AGGGTC       *GGGTCT        *GGTCTG         *GTCTGTand          *TCTGTC.

By detecting hybridization between the target and each of the aboveprobes, one can determine that the target molecule has the sequence ofthe reference sequence. One can also determine a hybridization patternto identify the sequence signature.

An array that contained probe sets defining all degenerate sequencesencoding RRGSV (SEQ ID NO:39) also would contain a probe set definingthe sequence CGCCGAGGGTCCGGG (SEQ ID NO:41). It would hybridize to thetarget molecule as shown with an asterisk:

Signature:  R  R  S  V  G (SEQ ID NO: 39) Target: CGACGAGGGTCTGTC,(SEQ ID NO: 40) Reference: CGCCGAGGGTCCGGG, (SEQ ID NO: 41) Probes:CGCCGA  GCCGAG   CCGAGG   *CGAGGG    *GAGGGT     *AGGGTC       GGGTCC       GGTCCG         GTCCGG and          TCCGGG.

Thus, upon detecting hybridization between the target and this probeset, one can determine that the target does not have this completereference sequence, or is related to a sequence signature although itencodes the sequence RS.

The target may hybridize to part of a reference nucleotide sequence butit may not hybridize at positions representing particular codons. Inthis case, the target does not encode the polypeptide sequencesignature, but may encode a related sequence signature which varies fromthe original as a result of a variable amino acid position. If the arraycontains probes defining sequence signatures that include such variablepositions, the computer system can process the hybridization data fromthe probe sets defining these other sequence signatures, to determinewhether the target encodes one of these. If the target fails tohybridize to the probes defining a sequence signature, then the targetdoes not encode this sequence signature.

The array need not include probes defining the degenerate set ofnucleotide sequences encoding a polypeptide sequence signature. As analternative to a degenerate set of nucleotide sequences, one can providefor generic bases such as inosine or mixtures of A, C, T, G, and U atwhat corresponds to the third codon position. In addition, one canemploy footprint, molecular bar-coding, or other hybridization patternsto determine the presence of, absence of, or variance from the referencesequence signature.

In another embodiment of this method, the array further comprises probesets selected for standard tiling of a reference sequence. Suppose, forexample, that as a result of mutation, the target nucleic acid has thesequence CGA CGA tGG TCT GTC (SEQ ID NO:42), which encodes RRWSV (SEQ IDNO:43). A probe set that is standard tiled throughout the referencesequence may include probe sets that hybridize to the target as follows:

Signature:   R  R  S  V  G (SEQ ID NO: 39) Reference:  CGACGAGGGTCTGTC(SEQ ID NO: 40) Target:  CGACGAtGGTCTGTC (SEQ ID NO: 42) Probes: *CGACGA CGtCGA  CGgCGA  CGcCGA   GACGAG   GAaGAG   GAtGAG   GAgGAG    ACGAGG   ACaAGG    ACtAGG    ACcAGG     CGAGGG     CGtGGG     CGgGGG    CGcGGG      GAGGGT      GAaGGT     *GAtGGT      GAcGGT       AGGGTC      AGaGTC       AGtGTC       AGcGTC        GGGTCT        GGaTCT       GGtTCT        GGcTCT       *GGTCTG        GGaCTG        GGgCTG       GGcCTG       *GTCTGT        GTaTGT        GTtTGT        GTgTGT       *TCTGTC         TCaGTC         TCgGTC         TCcGTC.

From this information, one can determine that the target does not encodethe signature sequence, but has the sequence:

*CGACGA    *GAtGGT       *GGTCTG        *GTCTGT         *TCTGTC orCGACGAtGGTCTGTC, which encodes (SEQ ID NO: 42)  R  R  W  S  V.(SEQ ID NO: 43

Software such as the GeneChip® software from Affymetrix, Inc. (SantaClara, Calif., USA) can be used to analyze the hybridization data. Seealso International Publication No. WO 97/28212, European PatentApplication Publication No. EP 0717113A2 (European Patent ApplicationNo. 95307476.2).

2. Screening for Members of a Gene Family

In another aspect, this invention provides methods for determiningwhether a target nucleic acid molecule encodes a member of a genefamily. This method is useful for determining whether a target moleculeis a known member of a family, or a new, previously unknown, member. Inselecting arrays for this type of screening, several parameters can bevaried.

One parameter is the number of gene family members whose sequences areused on the array. Probe sets defining sequences from at least one andmore preferably at least two members of the family are used on thearray. However, for the identification of new family members, onepreferably creates arrays containing probe sets defining sequences fromall known members of the family.

Another parameter that can be varied is the number of sequencesignatures from each member of the gene family that are defined by probesets on the array. A comparison of the amino acid and nucleotidesequences of known members of a gene family reveals both highlyconserved and variable sequence regions. Conserved regions, because theyshare a higher degree of identity between members, are more useful fordetermining whether a target encodes a member of the family. Variableregions, because they are the most distinct, are more useful fordiscriminating between members of the family and for indicating whethera target encodes a new member of the family. Accordingly, arrays usedfor screening members of a family contain probe sets defining at leastone sequence signature from each member of the gene family.

Another parameter that can be varied, related to the second parameter,is the number of nucleotide sequences within a degenerate set encodingan amino acid signature sequence from one or more of the gene familymembers from which probe sets are chosen. For example, a nucleic acidsignature sequence from a member of a gene family, if it is within thecoding region of the gene, encodes an amino acid sequence. Probe setscan be selected that define not only the reference nucleotide sequence,but members of the degenerate set that encode the same amino acidsequence as the reference nucleotide sequence. Such probe sets areuseful in identifying polymorphisms of any gene family member, as wellas new members of the family. Generic bases and probes having mixturesof bases at certain codon positions, such as the third codon positioncan also be employed.

Another parameter is the length of the sequence signature. While thereis no particular size limit, sequence signatures are preferably at least9 nucleotides long. A collection of sequence signatures totaling between75 and 125 nucleotides spread among about 4 signatures is particularlyuseful.

Any nucleic acid molecule can be used as a target molecule in thismethod. However, often, the target is a molecule that has beenpre-screened in accordance with the teachings of the present inventionso that there is reason to believe the target may be a member of thegene family. For example, one may screen a DNA library with probes(which can include degenerate sets, generic bases, and mixtures ofnucleotides at certain positions) having a sequence selected from one ormore members of the gene family. Depending upon the stringency of thehybridization conditions used, the probe may hybridize to sequences moreclosely or more distantly related to the probe. Thus, the targetsequence can be one that hybridizes under a selected set ofhybridization conditions to a probe having the reference sequence.

The hybridization data generated from a hybridization reaction betweenthe target and the probes on the array is processed to determine whetherthe data is consistent with the target nucleic acid being a member ofthe gene family. This can involve, for example, base calling the targetsequence over at least a sequence signature for a conserved region ofthe gene or the determination of whether the overall pattern expectedfor that sequence signature is present.

The hybridization data may indicate that the target molecule hassequences that are identical to that of a known member of the genefamily. However, if the hybridization data indicates that there aredifferences between the target sequence and the reference sequences, theextent of the differences provides further information about theidentity of the target sequence.

For example, if the differences are few enough, their location andidentity can in certain embodiments be determined by ID base callingusing, e.g., arrays that employ single increment, standard tiling. Inthis case, the information is consistent with the target being one ofthe known gene family members, possibly including allelic forms of thegene.

If there are significant differences between the target and the probesets, then the hybridization is generally quite weak in the regions thatdiffer. In this case, the target is identified as containing aninsertion that is not a previously known member of the family. Thepractitioner then can decide whether the clone is worth sequencing todetermine if it is actually a member of the family, and, if so, how itdiffers from the other members.

3. Screening for Gene Sequences

As we move into a world in which all the genes of the human and othergenomes are identified and sequenced, the focus of much nucleic acidanalyses will be the identification of which genes are present in aparticular sample. Such identification is particularly useful in thehierarchical methods of the present invention. Accordingly, thisinvention also provides methods of determining whether a target nucleicacid molecule has a nucleotide sequence from any of a set of genes. Themethods involve providing an array with probe sets defining sequencesignatures from the gene set. Hybridization data is collected from ahybridization reaction between the target and the probes on the array.The data is analyzed to determine whether the target contains thesequence signature of one of the genes in the set.

The hybridization data can be processed in the following manner. Theextent of hybridization between the probes that define each sequencesignature and the target can be determined. If the target has a sequenceclosely related to one of the sequence signatures, the degree ofhybridization between the target and the probe set that define thesequence signature of that gene will be strong compared to thehybridization signal with other sequence signatures defined in thearray. This assists in identifying sequence signatures in the target.Computerized methods for analyzing hybridization data from nucleic acidarrays are taught by WO97/29212; EP publication No. 95307476.2.

Preferably the sequence signatures are unique to the genes in the set. Asequence signature of about 20 nucleotides suffices in most cases touniquely identify a gene. The signature sequence can be from, forexample, a transcribed or coding region of the gene. Such arrays areuseful for example for determining the identity of target cDNAmolecules, variants of genomic clones.

One can obtain further information about a target sequence by providingarrays with probe sets in single-increment, standard tiling systems foreach nucleotide in each of the sequence signatures. In this case, whenthe target does not perfectly match a sequence signature, differencesbetween the two sequences can be determined by base calling.Alternatively, recognition of the hybridization pattern is employed.

B. Performing Hybridization Assays

Hybridization assays on substrate-bound polynucleotide arrays involve ahybridization step and a detection step. In the hybridization step, ahybridization mixture containing the target and, preferably, ahybridization optimizing agent, such as an isostabilizing agent,denaturing agent or renaturation accelerant, is brought into contactwith the probes of the array and incubated at a temperature and for atime appropriate to allow hybridization between the target and anycomplementary probes. Usually, unbound target molecules are then removedfrom the array by washing with a wash mixture that does not contain thetarget, such as hybridization buffer. This leaves only bound targetmolecules. In the detection step, the probes to which the target hashybridized are identified and the amount hybridized is determined by theintensity of the label. Since the nucleotide sequence of the probes ateach feature is known, identifying the locations at which the target hasbound provides information about the particular sequences of thesetargets.

The hybridization mixture includes the target nucleic acid molecule anda hybridization optimizing agent in an appropriate solution, i.e., ahybridization buffer. The target nucleic acid molecule is present in themixture at a concentration between about 0.005 nM and about 50 nMpreferably between about 0.5 nM and 5 nM or, more preferably, about 1 nMand 2 nM. The target nucleic acid molecule preferably includes adetectable label, such as a fluorescent or other type of label which canattach to the bound target (i.e. biotin).

Betaines and lower tetraalkyl ammonium salts are examples ofisostabilizing agents. Denaturing agents are compositions that lower themelting temperature of double stranded nucleic acid molecules byinterfering with hydrogen bonding between bases in a double-strandednucleic acid or the hydration of nucleic acid molecules. Denaturingagents include formamide, formaldehyde, DMSO (“dimethylsulfoxide”),tetraethyl acetate, urea, GuSCN, glycerol and chaotropic salts.Hybridization accelerants include heterogenous nuclear ribonucleoprotein(“hnRP”) A1 and cationic detergents such as, preferably, CTAB(“cetyltrimethylammonium bromide”) and DTAB (“dodecyl trimethylammoniumbromide”), and, also, polylysine, spermine, spermidine, single strandedbinding protein (“SSB”), phage T4 gene 32 protein and a mixture ofammonium acetate and ethanol.

The hybridization mixture is placed in contact with the array andincubated. Contact can take place in any suitable container, forexample, a dish or a cell specially designed to hold the array and toallow introduction of the fluid into and removal of it from the cell soas to contact the array. Generally, incubation will be at temperaturesnormally used for hybridization of nucleic acids, for example, betweenabout 20° C. and about 75° C., e.g., about 25° C., about 30° C., about35° C., about 40° C., about 45° C., about 50° C., about 55° C., about60° C. or about 65° C. For probes longer than about 14 nucleotides, 20°C.-50° C. is preferred. For shorter probes, lower temperatures arepreferred. The target is incubated with the probe array for a timesufficient to allow the desired level of hybridization between thetarget and any complementary probes in the array. Using a hybridizationtemperature of 25° C. can yield a very clear signal, usually in at least30 minutes to two hours, but it may be desirable to hybridize longer,i.e., about 15 hours.

After incubation with the hybridization mixture, the array usually iswashed with the hybridization buffer, which also can include thehybridization optimizing agent. These agents can be included in the samerange of amounts as for the hybridization step, or they can beeliminated altogether. Then the array can be examined to identify theprobes to which the target has hybridized.

C. Preparation of Target Samples

The target polynucleotide whose sequence is to be determined can beisolated from a clone, a cDNA, genomic DNA, RNA, cultured cells, or atissue sample. If the target is genomic, the sample may be from anytissue (except exclusively red blood cells). For example, whole blood,peripheral blood lymphocytes or PBMC, skin, hair or semen are convenientsources of clinical samples. These sources are also suitable if thetarget is RNA. Blood and other body fluids are also a convenient sourcefor isolating viral nucleic acids. If the target is mRNA, the sample isobtained from a tissue in which the mRNA is expressed. If thepolynucleotide in the sample is RNA, it is usually, though not always,reverse transcribed to DNA. DNA samples or cDNA resulting from reversetranscription are usually amplified, e.g., by PCR. Depending on theselection of primers and amplifying enzyme(s), the amplification productcan be RNA or DNA. Paired primers are selected to flank the borders of atarget polynucleotide of interest. More than one target can besimultaneously amplified by multiplex PCR in which multiple pairedprimers are employed. If the target is a long polynucleotide, it may beappropriate to fragment the target into smaller pieces before performingthe hybridization reaction. As used herein, the detection ofhybridization between a target and probes on an array includesperforming the hybridization reaction with all or portions of thetarget.

The target can be labeled at one or more nucleotides during or afteramplification. For some target polynucleotides (depending on size ofsample), e.g., episomal DNA, sufficient DNA is present in the tissuesample to dispense with the amplification step. Preferred labels includefluorescent labels, chemi-luminescent labels, bio-luminescent labels,and calorimetric labels, among others. Most preferably, the label is afluorescent label such as a fluorescein, a rhodamine, a polymethine dyederivative, a phosphor, and so forth. Commercially available fluorescentlabels include, inter alia, fluorescein phosphoramidites such asFluoreprime (Pharmacia, Piscataway, N.J.), Fluoredite (Millipore,Bedford, Mass.) and FAM (ABI, Foster City, Calif.).

Useful light scattering labels include large colloids, and especiallythe metal colloids such as those from gold, selenium, silver, tin, andtitanium oxide.

Radioactive labels include, for example, ³²P This label can be detectedby a phosphorimager. Detection, of course, depends on the resolution ofthe imager. Phosophorimagers are available having resolution of 50microns. Accordingly, this label is currently useful with chips havingfeatures of at least that size.

In one embodiment, biotinylated bases are incorporated into the targetnucleic acid. Hybridization is detected by staining withstreptavidin-phycoerythrin.

When the target strand is prepared in single-stranded form as inpreparation of target RNA, the sense of the strand should of course becomplementary to that of the probes on the chip. This is achieved as anexample by appropriate selection of primers used for any amplificationof the target. Also, the array can contain probes for both strands.

The target is preferably fragmented before application to the chip toreduce or eliminate the formation of secondary structures in the targetand reduce any overhang interaction. The average length of the targetsegments following hybridization is usually longer than the length ofthe probes on the chip.

D. Substrate-Associated Polynucleotide Arrays

Substrate-associated polynucleotide arrays used in the assays of thisinvention typically include between about 5×10² and about 10⁸ featuresper square centimeter, or between about 10⁴ and about 10⁷, or betweenabout 10⁵ and 10⁶.

Preferably, the arrays are produced through spatially directedpolynucleotide synthesis. As used herein, “spatially directedpolynucleotide synthesis” refers to any method of directing thesynthesis of a polynucleotide to a specific location on a substrate.Methods for spatially directed polynucleotide synthesis include, withoutlimitation, light-directed polynucleotide synthesis, microlithography,application by ink jet, microchannel deposition to specific locationsand sequestration with physical barriers. In general these methodsinvolve generating active sites, usually by removing protective groups;and coupling to the active site a nucleotide which, itself, optionallyhas a protected active site if further nucleotide coupling is desired.

In one embodiment substrate-bound polynucleotide arrays are synthesizedat specific locations by light-directed polynucleotide synthesis. Thepioneering techniques of this method are disclosed in U.S. Pat. No.5,143,854; PCT WO 92/10092; PCT WO 90/15070; and U.S. application Ser.Nos. 08/249,188, filed May 24, 1994, 07/624,120, filed Dec. 6, 1990, and08/082,937, filed Jun. 25, 1993. In a basic strategy of this process,the surface of a solid support modified with linkers and photolabileprotecting groups is illuminated through a photolithographic mask,yielding reactive hydroxyl groups in the illuminated regions. A3′-O-phosphoramidite-activated deoxynucleoside (protected at the5′-hydroxyl with a photolabile group) is then presented to the surfaceand coupling occurs at sites that were exposed to light. Following theoptional capping of unreacted active sites and oxidation, the substrateis rinsed and the surface is illuminated through a second mask, toexpose additional hydroxyl groups for coupling to the linker. A second5′-protected, 3′-O-phosphoramidite-activated deoxynucleoside (C-X) ispresented to the surface. The selective photodeprotection and couplingcycles are repeated until the desired set of products is obtained.Photolabile groups are then optionally removed and the sequence is,thereafter, optionally capped. Side chain protective groups, if present,are also removed. Since photolithography is used, the process can beminiaturized to generate high-density arrays of polynucleotide probes.

This general process can be modified. For example, the nucleotides canbe natural nucleotides, chemically modified nucleotides or nucleotideanalogs, as long as they have activated hydroxyl groups compatible withthe linking chemistry. The protective groups can, themselves, bephotolabile. Alternatively, the protective groups can be labile undercertain chemical conditions, e.g., acid. In this example, the surface ofthe solid support can contain a composition that generates acids uponexposure to light.

Thus, exposure of a region of the substrate to light generates acids inthat region that remove the protective groups in the exposed region.Also, the synthesis method can use 3′-protected5′-O-phosphoramidite-activated deoxynucleoside. In this case, thepolynucleotide is synthesized in the 5′ to 3′ direction, which resultsin a free 5′ end.

The general process of removing protective groups by exposure to light,coupling nucleotides (optionally competent for further coupling) to theexposed active sites, and optionally capping unreacted sites is referredto herein as “light-directed nucleotide coupling.”

Tiling strategies for creating probe arrays adapted for various tasks,such as re-sequencing are described in U.S. patent application Ser. No.08/510,521, filed Aug. 2, 1995 and International applicationPCT/US94/12305, filed Oct. 26, 1994.

If desired, the substrate-bound polynucleotide array can beappropriately packaged for use in a chip reader. One such apparatus isdisclosed in International Publication No. WO 95/33846.

Probes may be laid out on a polynucleotide array with a specificallydefined positional relationship. For example, the probes in the set canbe positioned in adjacent features on the array. However, hybridizationdata from a polynucleotide array normally will be processed by aprogrammable digital computer. The computer memory can be programmed toremember the sequence of each probe at each feature on the array.Consequently, one may provide a polynucleotide array or setpolynucleotide arrays containing all possible sequences of probes of agiven length. For example, a chip having 525 by 525, or 275,625,features can contain all nine-mer probes having all possible nucleotidesequences of 9 nucleotides (4⁹=262,144). Using any selected tilingstrategy, the programmable computer can identify the set of featurescontaining probes that define any given reference sequence.

Then, the computer can be programmed to process hybridization data fromthe probe set that defines a reference sequence.

E. Detecting Fluorescently Labeled Probes

Determining a signal generated from a detectable label on an arrayrequires a polynucleotide array or chip reader.

The nature of the polynucleotide array reader depends upon theparticular type of label attached to the target molecules.

In one embodiment the chip reader comprises a body for immobilizing thepolynucleotide array. Excitation radiation, from an excitation sourcehaving a first wavelength, passes through excitation optics from belowthe array. The excitation optics cause the excitation radiation toexcite a region of a polynucleotide array on the substrate. In response,labeled material on the sample emits radiation which has a wavelengththat is different from the excitation wavelength. Collection optics,also below the array, then collect the emission from the sample andimage it onto a detector. The detector generates a signal proportionalto the amount of radiation sensed thereon. The signals can be assembledto represent an image associated with the plurality of regions fromwhich the emission originated.

According to one embodiment, a multi-axis translation stage moves thepolynucleotide array in order to position different areas to be scanned,and to allow different locations of an array to be interrogated. As aresult, a 2-dimensional image of the polynucleotide array is obtained.

The polynucleotide array reader can include an auto-focusing feature tomaintain the sample in the focal plane of the excitation lightthroughout the scanning process. Further, a temperature controller maybe employed to maintain the sample at a specific temperature while it isbeing scanned. The multi-axis translation stage, temperature controller,auto-focusing feature, and electronics associated with imaging and datacollection are managed by an appropriately programmed digital computer.

In one embodiment, a beam is focused onto a spot of about 2 μm indiameter on the surface of the array using, for example, the objectivelens of a microscope or other optical means to control beam diameter.(See, e.g., U.S. patent application Ser. No. 08/195,889, filed Feb. 10,1994).

In another embodiment, fluorescent probes are employed in combinationwith CCD imaging systems. Details of this method are described in U.S.application Ser. No. 08/301,051, filed Sep. 2, 1994. In manycommercially available microplate readers, typically the light source isplaced above an array, and a photodiode detector is below the array. Forthe present methods, the light source can be replaced with a higherpower lamp or laser. In one embodiment, the standard absorption geometryis used, but the photodiode detector is replaced with a CCD camera andimaging optics to allow rapid imaging of the array. A series of Ramanholographic or notch filters can be used in the optical path toeliminate the excitation light while allowing the emission to pass tothe detector. In a variation of this method, a fiber optic imagingbundle is utilized to bring the light to the CCD detector. In anotherembodiment, the laser is placed below the polynucleotide array and lightdirected through the transparent wafer or base that forms the bottom ofthe polynucleotide array. In another embodiment, the CCD array is builtinto the wafer of the polynucleotide array.

The choice of the CCD array will depend on the number of polynucleotidesin each array. If 2500 features of sequence-specific polynucleotidesnominally arranged in a square (50×50) are examined, and 6 lines in eachfeature are sampled to obtain a good image, then a CCD array of 300×300pixels is desirable in this area. However, if an individual array has48,400 features (220×220) then a CCD array with 1320×1320 pixels isdesirable. CCD detectors are commercially available from, e.g.,Princeton Instruments, which can meet either of these requirements.

The detection device also can include a line scanner, as described inU.S. patent application Ser. No. 08/301,051, filed Sep. 2, 1994.Excitation optics focuses excitation light to a line at a sample,simultaneously scanning or imaging a strip of the sample. Surface-boundfluorescent labels from the array fluoresce in response to the light.Collection optics image the emission onto a linear array of lightdetectors. By employing confocal techniques, substantially only emissionfrom the light's focal plane is imaged. Once a strip has been scanned,the data representing the 1-dimensional image are stored in the memoryof a computer. According to one embodiment, a multi-axis translationstage moves the device at a constant velocity to continuously integrateand process data. Alternatively, galvometric scanners or rotatingpolyhedral mirrors may be employed to scan the excitation light acrossthe sample. As a result, a 2-dimensional image of the sample isobtained.

In another embodiment, collection optics direct the emission to aspectrograph which images an emission spectrum onto a 2-dimensionalarray of light detectors. By using a spectrograph, a full spectrallyresolved image of the array is obtained.

The read time for a polynucleotide array will depend on the photophysicsof the fluorophore (i.e., fluorescence quantum yield andphotodestruction yield) as well as the sensitivity of the detector. Forfluorescein, sufficient signal-to-noise to read a chip image with a CCDdetector can be obtained in about 30 seconds using 3 mW/cm² and 488 nmexcitation from an Ar ion laser or lamp. By increasing the laser power,and switching to dyes such as CY3 or CY5 which have lowerphotodestruction yields and whose emission more closely matches thesensitivity maximum of the CCD detector, one easily is able to read eacharray in less than 5 seconds.

F. Data Analysis

Data generated in hybridization assays is most easily analyzed with theuse of a programmable digital computer. The computer program generallycontains a readable medium that stores the codes. Certain files aredevoted to memory that includes the location of each feature and thesequence of the polynucleotide probe at that feature. Because analysisoften involves comparing the sequence of a target to a referencesequence, the program also can include in its memory the referencesequence. Using this information, the program can then identify the setof features on the array whose probes define the reference sequence inthe selected tiling strategy. The computer also contains code thatreceives as input hybridization data from a hybridization reactionbetween a target nucleic acid molecule and polynucleotide probes in thepolynucleotide array. The computer also contains code that processes thehybridization data. The computer program also can include code thatreceives instructions from a programmer as input.

The computer can transform the data into another format forpresentation. Data analysis can include the steps of determining, e.g.,fluorescent intensity as a function of substrate position from the datacollected, removing “outliers” (data deviating from a predeterminedstatistical distribution), and calculating the relative extent ofbinding of the targets from the remaining data. The resulting data canbe displayed as an image with color in each region varying according tothe light emission or extent of binding between targets and probestherein.

One application of this system when coupled with the CCD imaging systemthat speeds performance when the detection step involves hybridizationof a labeled target polynucleotide with a polynucleotide in the array isto obtain results of the assay by examining the on- or off-rates of thehybridization. In one version of this method, the amount of binding ateach address is determined at several time points after the targets arecontacted with the array. The amount of total hybridization can bedetermined as a function of the kinetics of binding based on the amountof binding at each time point. Thus, it is not necessary to wait forequilibrium to be reached. The dependence of the hybridization rate fordifferent polynucleotides on temperature, sample agitation, washingconditions (e.g., pH, solvent characteristics, temperature) can easilybe determined in order to maximize the conditions for rate andsignal-to-noise. Alternative methods are described in Fodor et al., U.S.Pat. No. 5,324,633, incorporated herein by reference.

The dependence of the hybridization rate for different polynucleotideson temperature, sample agitation, washing conditions (e.g., pH, solventcharacteristics, temperature) can easily be determined in order tomaximize the conditions for rate and signal-to-noise.

G. Mechanics of Assays

Assays on polynucleotide arrays generally include contacting apolynucleotide array with a labeled sample under the selected reactionconditions, optionally washing the array to remove unreacted molecules,and analyzing the biological array for evidence of reaction betweentarget molecules the probes. These steps involve handling fluids.

These steps can be automated using automated fluid handling systems forconcurrently performing the detection steps on the array. Fluid handlingallows uniform treatment of samples in the wells. Microtiter robotic andfluid-handling devices are available commercially, for example, fromTecan AG.

The chip can be manipulated by a fluid-handling device. This roboticdevice can be programmed to set appropriate reaction conditions, such astemperature, add reagents to the chip, incubate the chip for anappropriate time, remove unreacted material, wash the chip substrate,add reaction substrates as appropriate and perform detection assays. Theparticulars of the reaction conditions are chosen depends upon thepurpose of the assay, for example hybridization of a probe or attachmentof a label to polynucleotides.

If desired, the chip can be appropriately packaged for use in chipreader. One such apparatus is disclosed in U.S. patent application Ser.No. 08/255,682, filed Jun. 8, 1994.

H. Substrate-associated Polynucleotide Array Manufacture

In making a chip, the substrate and its surface preferably form a rigidsupport on which the sample can be formed. The substrate and its surfaceare also chosen to provide appropriate light-absorbing characteristics.For instance, the substrate may be functionalized glass, Si, Ge, GaAs,GaP, SiO₂, SiN₄, modified silicon, or any one of a wide variety of gelsor polymers such as (poly)tetrafluoro-ethylene,(poly)vinylidenedifluoride, polystyrene, polycarbonate, or combinationsthereof. Other substrate materials will be readily apparent to thoseskilled in the art upon review of this disclosure. In a preferredembodiment the substrate is flat glass or silica.

Surfaces on the solid substrate usually, though not always, are composedof the same material as the substrate.

Thus, the surface may be composed of any of a wide variety of materials,for example, polymers, plastics, resins, polysaccharides, silica orsilica-based materials, carbon, metals, inorganic glasses, membranes, orany of the above-listed substrate materials. In one embodiment, thesurface will be optically transparent and will have surface Si—OHfunctionalities, such as those found on silica surfaces.

Preferably, polynucleotides are arrayed on a chip in addressable rowsand columns. Technologies already have been developed to readinformation from such arrays. The amount of information that can bestored on each chip depends on the lithographic density which is used tosynthesize the wafer. For example, if each feature size is about 100microns on a side, each chip can have about 10,000 probe addresses(features) in a 1 cm² area.

The following examples are offered by way of illustration, not by way oflimitation.

EXAMPLE

The method of the invention was used to screen for new members of theTGF-β superfamily of proteins. There are currently 32 known members ofthis family. Clone libraries were created from genomic material based onhybridization to nucleic acid probes in solution that contain sequencescomplementary to sequence motifs that are indicative of members of thisgene family. The genomic inserts were approximately 15 kb in size. Mostof the inserts contain sequences from previously known members of thefamily.

Conventional approaches involve sequencing these 15 kb inserts over andover, most of the time only to find that the insert contains a familymember that has already been identified. The method of this inventionreplaced those laborious and time consuming steps with a faster, easierscreening method that can identify which clones contain known members ofthe family, and which few clones out of the large library are worthinvestigating in greater detail.

TGF-β Clone Screening Polynucleotide Array:

The array contained over 12,000 features with different probes withsingle-increment, 4-base trellis tilings for 99 bases for each of the 32known members of the TGF-β family (see FIG. 5). The 99 bases were from 4different regions of the genes and the contiguous regions range in sizefrom 18 to 30 bases. The interrogated regions were chosen based on a fewcriteria: they include regions that are (a) reasonably well conserved(highly conserved at the amino acid level, but less so at the DNA level)and that serve as identifiers of the protein family, (b) highly variableand serve as unique identifiers of individual members of the family, and(c) not near expected intron/exon boundaries.

TGF-β Clone Samples for Hybridization:

Either DNA or RNA can be produced from a clone using standard methods,e.g., nucleic acid extractions followed by PCR or in vitrotranscription, with labeled bases incorporated during the polymerizationstep. Fragmented single-stranded DNA or RNA can be used in thehybridization as well as fragmented double stranded DNA. Thehybridizations are done in either 6×SSPE-T or 3M TMACl-T (buffered withTris to avoid having any Na ions in the hybridization solution), andgenerally at temperatures above 30° C. to improve discrimination and toreduce cross-hybridization (this is more important in this applicationthan for some re-sequencing applications because the samples include˜15,000 bases). If labeled RNA is used, samples are fragmented with heatin the presence of Mg²⁺. If DNA is used, samples are fragmented bytreatment with DNAse I prior to hybridization. This works with bothdouble stranded DNA or with DNA that is made single-stranded followingPCR by degradation of one of the strands using lambda exonuclease.

Examples and Data Analysis:

Following hybridization and reading of the arrays, the images wereanalyzed using the TGF report GeneChip software (Affymetrix, Inc., SantaClara, Calif., USA). Base calls were made over all 99 bases for each ofthe 32 different regions. The calls were compared with the sequencesexpected for each of the 32 known wild type sequences (see FIGS. 5 and6). For each, the results of the base calling were listed, and theoutput was sorted based on the number of calls (# correct) that matchthe expected sequence in that region. In all the cases to date, whenknown sequences have been hybridized, the correct sequence was at thetop of the list. Additionally, the software gives a detailed assessmentof the base calls in each of the four different regions for the top fivesequences in the list, giving a clearer picture of where thesimilarities and differences occur. Result of hybridization between thearray and DNA from hBMP-7 and hBMP-5 is shown in FIG. 6.

Diagnosis of a disease is made by obtaining a sample of bodily fluids,tissue, or other nucleic-acid containing material and determines whethera sequence signature present in a possible pathogen or set of pathogensis present. For example, one determining whether a sequence signature ofa mycobacterium is also present in the sample using the methods taughton PCT publication no. WO97/29212.

If no mycobacterium is present, the presence of another suspectedpathogen is explored.

The present invention provides a novel method for performing assays onpolynucleotide arrays. While specific examples have been provided, theabove description is illustrative and not restrictive. Many variationsof the invention will become apparent to those of skill in the art uponreview of this specification. The scope of the invention should,therefore, be determined not with reference to the above description,but instead should be determined with reference to the appended claimsalong with their full scope of equivalents.

All publications and patent documents cited in this application areincorporated by reference in their entirety for all purposes to the sameextent as if each individual publication or patent document were soindividually denoted.

1. A method for determining whether a nucleic acid sample from a patientcontains nucleic acid encoding a signature sequence characteristic of apathogen said method comprising: obtaining a nucleic acid containingsample from said patient; providing a probe array comprising a firstplurality of polynucleotide probe sets each probe set defining adifferent reference nucleotide sequence wherein each referencenucleotide sequence signature is between 15 and 30 bases in length andcodes for a different amino acid sequence that is a signature sequencecharacteristic of said pathogen; and a second plurality ofpolynucleotide probe sets each probe set defining a degenerate set ofnucleotide sequences encoding each different amino acid sequence andwherein the probe set defining said degenerate set comprises at least25% of the nucleotide sequences encoding said degenerate set;hybridizing said nucleic acid sample to said probe array to generate ahybridization pattern; and analyzing said hybridization pattern todetermine if nucleic acid encoding a sequence signature characteristicof said pathogen is present in the sample.
 2. The method of claim 1,wherein the probe set defining said degenerate set of nucleotidesequences comprises at least 50% of the degenerate set of nucleotidesequences encoding each different amino acid sequence.
 3. The method ofclaim 1, wherein the probe set defining said degenerate set ofnucleotide sequences comprises at least 75% of the degenerate set ofnucleotide sequences encoding each different amino acid sequence.
 4. Themethod of claim 1, wherein the probe set defining said degenerate set ofnucleotide sequences comprises at least 95% of the degenerate set ofnucleotide sequences encoding each different amino acid sequence.
 5. Themethod of claim 1, wherein the pathogen is a mycobacterium.
 6. A methodfor determining whether a sample from a human patient has a sequencefrom a member of a gene family characteristic of a pathogen comprising:obtaining a sample comprising nucleic acid from said human patient;providing a polynucleotide probe array comprising, for each of at leasttwo different members of the gene family, a set of polynucleotide probesthat define a reference nucleotide sequence from the member of the genefamily; hybridizing said sample comprising nucleic acid to said probearray to generate a hybridization pattern comprising hybridization data;and processing the hybridization data to determine if the referencenucleotide sequence from one of the members of the gene family ispresent in the nucleic acid sample.
 7. The method of claim 6 wherein thestep of processing is performed by a programmable digital computer. 8.The method of claim 6 wherein the polynucleotide probe array furthercomprises, for each of the members of the gene family, a probe setdefining a highly conserved region of the gene and a probe set defininga highly variable region of the gene.
 9. The method of claim 6 whereinthe polynucleotide probe array further comprises, for each of themembers of the gene family, probe sets defining at least two highlyconserved regions of the gene and probe sets defining at least twohighly variable regions of the gene.
 10. The method of claim 6 whereinthe reference nucleotide sequence codes for an amino acid sequence andthe array further comprises probe sets defining the degenerate set ofnucleotide sequences encoding the amino acid sequence.
 11. The method ofclaim 6, wherein the reference nucleotide sequence is a highly conservedregion of the gene family.
 12. The method of claim 6, wherein saidreference nucleotide sequence is between 9 and 100 nucleotides inlength.
 13. The method of claim 6 wherein the probe array has a densityof at least four hundred different polynucleotides sequences per squarecentimeter.
 14. The method of claim 6 wherein the pathogen is amycobacterium.